A common type of ink jet printer uses replaceable ink supplies that provide ink to tiny nozzles, or orifices, which form the ink into micro-droplets and eject the ink onto a print media. Ink jet nozzle droplet generators such as piezoelectric transducers or wave propagators can be used in ink jet systems. With most ink jet equipment, the ink ejector or pen is typically mounted on a carriage, which scans across the print media. As the carriage scans, the micro-droplets are deposited onto the print media via a print head.
The ink jet pen may have a self-contained reservoir attached for storing and providing appropriate amounts of ink to the printhead during a printing cycle. These self-contained reservoirs are commonly referred to as ink cartridges. If reusable semi-permanent, or permanent pens rather than print cartridges are employed, ink is either supplied from remote ink containers or the ink container is mounted on the carriage with the pen.
Most ink jet printers can supply both color ink and black ink. To provide a color printing capability, ink cartridges or containers for each color can supply colored ink to a print head which mixes the colors on the print media to obtain a desired hue and shade. Similarly, black ink can be supplied from a black ink cartridge or container to a print head, which then deposits the ink onto the print media to generate the desired shade of gray or black.
To prevent ink leakage from a typical ink jet printing system that utilizes one or more ink reservoir containers, it is common to exert a force on the ink to retain it within the ink reservoir. For example, many ink reservoirs contain a capillary medium, such as foam (or an ink sponge), which is capable of absorbing and retaining ink. The capillarity of the capillary medium exerts a force (capillary force) that draws the ink into the capillary medium, preventing the ink from leaking out of the capillary medium and thus the reservoir. Many ink reservoirs initially contain enough ink to wet the capillary medium up to a percentage of the height of the capillary medium (e.g., 75 to 95 percent) with the remaining upper portion of the capillary medium containing air, for example. Moreover, ink reservoirs often include an air-filled space between the top of the capillary medium and a cover of the ink reservoir.
Capillary medium-based ink reservoirs are typically vented to atmospheric pressure to prevent excessive negative (e.g., vacuum type) pressures within the reservoir that can reduce or prevent ink flow to the print head. Venting is often provided by a vent disposed in the cover of the ink reservoir. In this situation, air may flow through the vent between an atmosphere surrounding an exterior of the ink reservoir and an interior of the ink reservoir. In addition, venting relieves pressure buildups that can occur when an ink reservoir is exposed to extreme environmental conditions. For example, extreme conditions may be encountered during shipping, such as high temperatures in motor vehicles or low pressures in airplanes at high altitudes. In such situations, air flows through the vent between the interior of the ink reservoir and the atmosphere surrounding the exterior of the ink reservoir.
In some situations, air becomes trapped in the capillary medium (e.g., while adding ink to the ink reservoir) and forms air pockets or voids within the capillary medium. This situation is amplified for applications involving hydrophilic capillary media because hydrophilic capillary media normally do not require a vacuum during filling. Moreover, when the ink reservoir is subjected to stresses during shipping and/or handling, such as dropping the ink reservoir, the volume of entrapped air can increase or air from the space above the capillary medium can be displaced into the capillary medium. The air within the capillary medium may lead to failure when the ink reservoir is exposed to high temperatures and/or low pressures. In particular, the high temperatures and/or low pressures cause the air within the capillary medium to expand and force ink out of the vent instead of air.
If ink is expelled during shipping, the expelled ink can contaminate the exterior of the ink container and any surrounding packaging. Expelled ink can also interact with the characteristics of the ink in the reservoir and degrade overall print quality. Additionally, expelled ink in multi-colored containers may contaminate the other colors.